1. Field of the Invention
The present invention relates to a programmable industrial controller configured to measure the critical dimensions of a part while the part is passing through a progressive die machine.
2. Description of the Related Art
Traditionally, progressive die machines include an upper die that is reciprocally moveable with respect to the lower die. A motor imparts rotational motion to the output shaft that, in turn, rotates a eccentrically-mounted pin on a concentrically-mounted plate on an output shaft, thereby tracing a circular path. The rotational motion, in turn, results in a ram mounted on an upper surface of the die to move reciprocally with respect to the lower die.
A rotation of the output shaft of the motor is a xe2x80x9cstrokexe2x80x9d of the machine that ranges from 0 to 360 degrees. The point at which the pin on the plate of the motor output shaft is located at the uppermost vertical position with respect to the plate is the xe2x80x9czero positionxe2x80x9d or xe2x80x9ctop dead centerxe2x80x9d. At the top dead center position, the upper die is positioned with the greatest extent above the lower die. The point at which the pin on the plate of the motor output shaft is located adjacent to the lowermost vertical position with respect to the plate is the xe2x80x9c180 degree positionxe2x80x9d. In the 180 degree position, the upper die is positioned adjacent to the lower die and this is the position whereby the forming operations are performed on the web. Between the 0 and 180 degree positions, the upper die is lowered with respect to the lower die and between the 180 and 360 degree positions, the upper die is raised with respect to the lower die.
The upper and lower dies cooperate to define several forming stations therein. Each forming station includes an individual forming tool and a die which are configured and dimensioned so that a particular predetermined operation can be performed on the web fed between the upper and lower dies. The web is typically an elongated strip of material provided as a feedable supply adjacent the machine, such as on a spool. The progressive die machine typically includes a feeding apparatus mounted adjacent the lower die which sequentially advances the web between the upper and lower dies and through each of the forming stations therein.
The number of forming stations is determined by the number of forming operations necessary to form a desired part. A portion of each of the forming tools is located on the upper die and are driven in unison in reciprocal fashion by the ram. Therefore, a forming operation is performed at each forming station during each stroke of the ram.
Following each stroke, the web is advanced so that each portion of the web is positioned within the next successive forming station in the machine. When a portion of the web has passed each forming station in the progressive die machine, a desire part is formed. The last station in the machine typically includes a severing tool and a discharge chute. The severing tool cuts the formed part from the web so that the formed part can fall into the discharge chute and be accumulated therein.
Typically, progressive die machines are plagued with many uncontrollable problems resulting in formed parts that are not within a certain tolerance that have to be thrown away. In many cases, the tolerances that the parts must fall within are of a critical importance and a part that falls outside of the tolerances can cause a catastrophic failure in the system or machine in which the part is ultimately installed. In particular, progressive die machines often experience problems due to changes in the thickness of the web material from which the parts are formed, flaws in the web material, wear on the forming tools and dies, and foreign matter located on the web material. These problems cause the formation of unacceptable parts that often go undetected by the machine and/or its operator until the parts are ultimately manually measured as to whether they are within the specific tolerances.
Due to the difficulties associated with monitoring the formation of a part in a progressive die machine to ensure that all of the parts are within very specific tolerances prior to manufacturing a pile of malformed parts, there is a need for measurement system located within the die that is configured to test every part while it is still in the die to determine whether each part is within the specified tolerance range. There is also a need for a measurement system that is capable of operating within a high-speed press (e.g., 180 to 300 strokes/minute).
While there have been attempts in the past to measure parts in the die of a progressive die machine, these attempts have been either unsuccessful or cost-prohibitive. In particular, one such attempt involves the installation of several transducers including transformers and cores mounted therein on separate upper and lower bodies that are mounted onto the upper and lower dies, respectively. A separate transducer is a xe2x80x9ctrigger devicexe2x80x9d that signals the initiation of the measurement process and provides a xe2x80x9czeroxe2x80x9d reference plane for comparison with the remaining transducers. All of the transducers in both the upper and lower bodies must contact the part in order to generate an error signal indicative of whether the particular part is within acceptable tolerance limits. In this case, significant modifications to both the upper and lower dies are required in order to use this kind of measurement system. Unfortunately, these modifications are costly and difficult to make on a traditional progressive die machine. Thus, there is also a need for a part measurement system that requires only minor modifications to the standard progressive die machine.
Accordingly, one object of this invention is to provide a part measurement system that includes a press machine, a part measurement sensor and a press controller. The press machine includes a lower die coupled to an upper die, wherein the lower die includes a top surface supporting a strip of material to be formed into a part after a stripper plate coupled to the upper die contacts the strip of material. The part measurement sensor is located in the lower die and measures a critical dimension of the part while the part is in the lower die. The press controller is coupled to the press machine and the sensor, and controller processes a measurement signal from the part measurement sensor of the critical dimension of the part, compares the measurement signal to a predetermined threshold value, and generates a command signal to the press machine to either reject or accept the part.
Another object of this invention is to provide a part measurement system including a press machine having a lower die coupled to an upper die, wherein the lower die includes a top surface supporting a strip of material to be formed into a part after a stripper plate coupled to the upper die contacts the strip of material, a part measurement sensor located in the lower die, wherein the sensor measures a critical dimension of the part, and a press controller coupled to the press machine and the sensor, wherein the controller processes a measurement signal from the part measurement sensor of the critical dimension of the part, compares the measurement signal to a predetermined threshold value, and generates a command signal to the press machine to either reject or accept the part.
Yet another object of this invention is to provide a method of measuring a critical dimension of a part in a press machine. The method includes the steps of feeding a strip of material through the press machine, wherein the machine includes a lower die coupled to an upper die and the lower die includes a top surface supporting the strip of material, forming the strip of material into the part, wherein a stripper plate coupled to the upper die contacts the strip of material and the upper die punches the strip of material, measuring the critical dimension of the part with a part measurement sensor located in the lower die, and processing a measurement signal from the part measurement sensor of the critical dimension of the part, wherein a press controller compares the measurement signal to a predetermined threshold value, and generates a command signal to the press machine to either reject or accept the part.